1. Field Of The Invention
The invention relates to a liquid crystal display (LCD) driver and power supply, more particularly to an LCD display driver and power supply for the LCD display of a telephone dialing circuit.
2. Description Of The Related Art
Display drivers for the LCD display of a telephone dialing circuit are known in the art. However, the power supply for the LCD display is not the same power supply as that of the telephone dialing circuit because of incompatibility in voltage ratings. The usual power supply voltage of the telephone dialing circuit ranges from 2 to 5.5 volts, while the usual input voltage of an LCD display of a size used in ordinary calculators is approximately 3 volts. If a voltage of more than 3 volts is used to supply power to the liquid crystal display, problems concerning the illumination of the segments found on the LCD display arises. This is one reason why the input voltage supplied to the LCD display must be kept as stable as possible.
A simple solution to this problem is to reduce the power supply voltage to a value of 3 volts if the power supply voltage is greater than 3 volts. However, if the power supply voltage is 3 volts or less, further reduction cannot be done since an input voltage of less than 3 volts would not drive the LCD display.
This problem of not having the same power source for the LCD display and the telephone dialing circuit makes the present systems more expensive and, at the same time, takes up much more space than it would if the LCD display and the telephone dialing circuit have the same power supply.